As a web firm that provides three primary offerings for verbose CMS systems (Drupal, The Marketing Command Center, and WordPress) we find ourselves in a strange spot when talking to business owners about the future of developing their web presence. Most of our clients have very extended needs outside of what would be considered the "norm" in terms of functionality. This consideration matters more than ever which the largest core upgrade to Drupal that's ever taken place. Below I've listed out some core considerations when trying to make a tough decision on Drupal 6 or 7.

Drupal Platform Considerations

1. The Drupal 6 to 7 migration is more extensive than previous upgrades due to major changes in the platforms architecture. What this means is you can expect a larger financial impact in utilizing web firms to make the migration for you. Depending on the customization of your web presence and it's corresponding functionality this will mean different things for different clients.
2. Drupal 6 is still the only production ready version. It has a verbose community of modules and options that help reduce overall development time. With that being said the migration to Drupal 7 will make most of these modules unusable and they will need to be updated either by their core contributors or the web firm your working with.
3. Drupal 6 will still be supported by Drupal.org as they always support the most current version and the next version back. So when Drupal 7 becomes production ready, Drupal 6 will continue to be supported until version 8 makes it's way onto the scene. You'll still receive security patches and updates.
4. Drupal 7 will take some time to pioneer and new modules will take some time to create amongst the community. Drupal 7 should only be deployed for those that wish to pioneer new technology and accept the risks of additional custom development and break/fix situations that may occur on any untested platform.

What's My Best Option

 You've got two distinct options here. One favors the bold and if you're able to weather the storm you'll be able to muscle through Drupal 7 and not worry about upgrading the core of your content management system for quite some time. However, you'll need to be willing to accept the fact that open source modules may not be available to you for a bit of time and that bugs that may incur break/fix development fees could crop up in your web presence from time to time.

Your second options is to roll-out on production ready Drupal 6. The advantages are that you'll have reduced deployment costs and a stable working environment. The downside is that you'll need to set aside funds and look to the future in upgrading to Drupal 7 when the time is right.

We're always here to help so don't hesitate to reach out if you have any questions.